Question

You are a forensic scientist on a case of a missing child. You are tasked with using genetic genealogy to determine if a child in custody is the missing child. Currently, you do not have a DNA sample from the child. However, the child has hemophilia, a sex-linked genetic disorder passed from mother to child. Looking at the grandparents and parents of the missing child, you put together this pedigree. The shaded shapes mean the person has hemophilia. The open shapes mean a person does not have hemophilia and they are not a carrier of the disorder. The circles represent females, and the squares represent males in the family. The child in custody is represented with a shaded circle. Image of unshaded circle and shaded square at the top, an unshaded circle, square, then circle in the middle, then a shaded circle on the last row. Could the child in custody be the missing child? Yes, the mother or father could be hiding the hemophilia trait as carriers. Yes, since the grandfather has hemophilia, the granddaughter will have it. No, since the mother and father do not have hemophilia, their child could not. No, this is not the missing child because the mother does not carry the trait to pass on.

Answer 1

the child in custody could not be the missing child

Step-by-step explanation:

Hemophilia is a sex-linked recessive disorder, which means it’s carried on the X chromosome. Males have one X and one Y chromosome (XY), and females have two X chromosomes (XX). If a male inherits the X chromosome carrying the disorder from his mother, he will have hemophilia. A female would need to inherit two copies of the gene to have the disorder, one from each parent.

In your scenario, the grandfather has hemophilia, which means he carries the gene on his X chromosome. His daughter (the mother of the missing child) would have received this X chromosome, making her a carrier of the trait, even though she doesn’t show symptoms of the disorder.

The mother can pass on the X chromosome carrying the hemophilia gene to her children. If the child in custody is a girl (as indicated by the shaded circle), she would need to inherit the gene from both parents to have the disorder. However, the father does not have hemophilia, so he cannot pass on the gene. Therefore, the child in custody could not be the missing child based on the information provided.

Please note that this analysis assumes complete penetrance of the gene, no new mutations, and no non-paternity events. In real-world scenarios, genetic testing would be necessary to confirm these findings.